1. Technical Field
The invention relates to a sliding element, in particular a piston ring, having a coating on at least one running surface.
Sliding elements such as, for example, piston rings, pistons or cylinder liners in internal combustion engines must work throughout a long service life, both with as little friction as possible and with a low level of wear. The friction that is directly linked to fuel consumption in internal combustion engines can be kept low by DLC (diamond-like carbon) coatings. Furthermore, layer thicknesses of up to 40 μm can be achieved in principle. However, with layer thicknesses of more than 5 μm, there is the problem that the layer properties change, for example in respect of the structure and the composition of the layer, and therefore the required service life is not achieved. This applies analogously to layer thicknesses of less than 5 μm.
2. Related Art
Also known in this connection are PVD coatings based on a hard material, which mostly comprise chromium nitride. Although such layers do have the necessary resistance to wear, they nevertheless do not have the required low coefficients of friction.
A sliding element having a DLC coating with good run-in behavior is known from DE 10 2005 063 123 B3, Overall, however, the durability of a low coefficient of friction can be improved further.
DE 10 2008 016 864 relates to a sliding element having a coating which comprises, from the inside outwards, an adhesive layer, a metal-containing DLC layer and a metal-free DLC layer.
Known from DE 197 35 962 A1 is a guide bush and a method of forming a hard carbon film on the inner surface of the guide bush, in which a hard carbon film of hydrogenated amorphous carbon is formed on the inner surface by a plasma CVD process.
Finally, WO 2006/125683 A1 shows a piston ring comprising, from the inside outwards, a layer comprising an element of group IVB, VB or VIB, an intermediate layer comprising a diamond-like nanocomposite composition, and a DLC layer.
Applicant's not previously published DE 10 2009 028 504 relates to a sliding element.